Particles of insecticides used as seed treatments may deliver a fatal blow to honeybees in cornfields, researchers have found. The scientists say exposure of bees to the insecticides, known as neonicotinoids, may cause honeybee colony losses. But pesticide manufacturers contend that, under normal conditions, the treated seeds don’t pose a serious risk.

Seed coatings containing insecticides are popular with growers because only small amounts are required to protect young plants from pests. The neonicotinoids work by disrupting the nicotinic acetylcholine receptor of an insect’s nerve cells.

But starting in the late 1990s, beekeepers in Europe raised alarms about two neonicotinoids, clothianidin and imidacloprid, claiming they were to blame for sharp declines in honeybee colonies, now known as colony collapse disorder. As researcher Andrea Tapparo and colleagues at Italy’s University of Padua point out, in Europe, corn sowing from mid-March to May is often followed by a rapid disappearance of bees.

Earlier research showed that after treated corn is planted, the amount of pesticide residue in the soil is below 50 ppb, which is not high enough to cause acute toxicity in bees. Tapparo’s team looked instead at the amount of insecticide that falls to the ground and is released to the air during seed planting. Farmers use pneumatic machines that suck seeds out of a bin and blow them toward the ground. In the process, bits of the seed coating break off and can become airborne.

The team reports that measurements of air particulates and residue on dead bees at the time of planting indicated the bees’ levels of exposure to neonicotinoids were high and could explain colony losses (Environ. Sci. Technol., DOI: 10.1021/es2035152).

Seed treatments with neonicotinoids are manufactured by Bayer CropScience, BASF, and Monsanto. Utz Klages, head of external communications for Bayer CropScience, contends the study does not show the treated seeds cause colony collapse disorder. “The work of this research team demonstrates that lethal exposure of honeybees to abraded seed dust is only likely to occur under very specific and unusual conditions and provides a basis for further targeted efforts to limit the possibility of such occurrences,” he says. For example, the exposure may be reduced by improving the seed coatings and modifying the planting machines.

"Utz Klages, head of external communications for Bayer CropScience, contends the study does not show the treated seeds cause colony collapse disorder" - in the words of Mandy Rice Crispies, "well, he would say that wouldn't he?"

We've known for years how deadly neonicotinoids are to bees (and loads of other pollinators), but the companies concerned are making a fortune from them, and possess enormous "clout" (even to the heart of governments) - kerrrching!

Tapparo's findings mirror those of another study published this year by Krupke et al. in the journal PLoS ONE ...link below to abstract.
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0029268

And Jeff Pettis, Lead Scientist at the USDA Bee Research Laboratory in Beltsville, Maryland just published an article last month more clearly linking neonicotinoids to colony collapse disorder through sub-lethal exposure...that link is here.
http://www.springerlink.com/content/p1027164r403288u/

Further, Starner and Goh last month published a paper showing that imidacloprid was showing up in California surface waters at alarming levels potentially harmful to aquatic invertebrates. That link here...
http://www.springerlink.com/content/566t681j31233742/

As a scientist, the links are clear enough to me that there is a high likelyhood these compounds are detrimental to pollinating insects and all insects in both aquatic and terrestrial food chains.

These studies overlook the real world experiences of beekeepers and seed treated crops:

Canola is grown commercially mostly on the prairies in Canada. In 2008, 16.6 million acres (6.6 million ha) were planted and the acreage is expanding. There are 52,000 canola producers. Canada is the largest single producer of canola in the world.

Commercially grown canola is predominantly a prairie crop. It is so common that 80% of Canadaâs honey crop is from canola. This amounts to 50 million lb per year of Grade No 1 white honey.

Approximately 300,000 colonies harvest open pollinated canola. The expanding hybrid seed production industry, where farmers produce seed under contract to the seed companies, required 80,000 colonies in 2008 for pollination in southern Alberta.

Most canola seeds are now treated with systemic insecticides such as GauchoÂ® (imidacloprid), PonchoÂ® (chlothianidin) or HelixÂ® (thiamethoxan). Although there is an expressed concern by many beekeepers around the world about the use of systemics, the experience in Canada is that we have had 10 years of large scale use on canola with no observed ill effect.

Thank you for your comments. There seems to be an upwelling of research in this area, and I'm sure we'll have more on the topic to report. I do find it interesting that research suggests that certain planting/agronomy practices may increase (decrease?) possible impacts on bees from pesticides. Peter - thanks for the info about Canola growing in Canada- it sounds like the crop keeps bees quite busy.